As the solution above says this is given when you heal other people for a combined total of 100 health states across all matches. It is a running total and so it is unaffected by dying or anything like that. So no need to be overly cautious.
There are perks that can help with this. Empathy is great because it lets you see the auras of injured survivors. You can go find them and heal them with it easily. Just be weary that the killer may be on them. Botany knowledge will speed up healing by 33 percent at level 3. We'll Make It is really good for healing people right after you get them off a hook. I recommend running those three perks if you are specifically going for this achievement. Both Empathy and Botany knowledge are Claudette perks, so you can pick her and she will start with these at level one. We'll make it is a basic perk which means it will be available on all characters.
Bond is another perk that you could use in place of empathy if you want. It allows you to see all the other survivors within a certain radius (36 meters at tier three). I think empathy is better for trying to heal people, but if you don't have empathy, bond is a good secondary option.